The blow ellipes represents a convex lense. The x represents the focal point of the image. Because a convex lens has such a wierd shape it makes the image that is sent into the camera upsidown. In the applet we see that object is point D and when it goies through the lense the image will be placed at the intersection points of the rays.
Questions:
1) what happens when the point D(the object) get too close to the y axis?
2) From this applet what can we see about how light refracts through a lens?
3) what happens when you grab the focal point and drag it along the x axis?